// 选择年份
let year = document.getElementById("year");
let str_year = '';
for(let i=1900;i<2022;i++){
  str_year += `<option>${i}</option>`;
}
year.innerHTML = str_year;
// 选择月份
let month = document.getElementById("month");
let str_month = '';
for(let i=1;i<13;i++){
  if(i<10){
    i = "0"+i;
  }
  str_month += `<option>${i}</option>`;
}
month.innerHTML = str_month;
// 选择日期
let day = document.getElementById("day");
let str_day = '';
for(let i=1;i<32;i++){
  if(i<10){
    i = "0"+i;
  }
  str_day += `<option>${i}</option>`;
}
day.innerHTML = str_day;